GDF15, a member of the TGFβ family, is a secreted protein that circulates in plasma as a 25 kDa homodimer. Plasma levels of GDF15 range between 150 and 1150 pg/ml in most individuals (Tsai et al., J Cachexia Sarcopenia Muscle. 2012, 3: 239-243). Plasma levels of GDF15 are increased under conditions of injury, cardiovascular disease and certain types of cancer. This upregulation is thought to be a cytoprotective mechanism. High plasma levels of GDF15 are associated with weight loss due to anorexia and cachexia in cancer, and in renal and heart failure. In a clinical trial, GDF levels were an independent predictor of insulin resistance in obese, non-diabetic subjects (Kempf et al., Eur. J. Endo. 2012, 167: 671-678). A study in twins showed that the differences in levels of GDF15 within twin pairs correlated to the differences in BMI within that pair, suggesting that GDF15 serves as a long-term regulator of energy homeostasis (Tsai et al., PLoS One. 2015, 10(7):e0133362).
While GDF15 has been extensively studied as a biomarker for several cardiovascular and other disease states, a protective role for GDF15 has also been described in myocardial hypertrophy and ischemic injury (Collinson, Curr. Opin. Cardiol. 2014, 29: 366-371; Kempf et al., Nat. Med. 2011, 17: 581-589; Xu et al., Circ Res. 2006, 98:342-50). GDF15 was shown to play an important role in protection from renal tubular and interstitial damage in mouse models of type 1 and type 2 diabetes (Mazagova et al., Am. J. Physiol. Renal Physiol. 2013; 305: F1249-F1264). GDF15 is proposed to have a protective effect against age-related sensory and motor neuron loss, and it improves recovery consequent to peripheral nerve damage (Strelau et al., J. Neurosci. 2009, 29: 13640-13648; Mensching et al., Cell Tissue Res. 2012, 350: 225-238). In fact, GDF15 transgenic mice were shown to have a longer lifespan than their littermate controls, which can indicate that this molecule serves as a long-term survival factor (Wang et al., Aging. 2014, 6: 690-700).
Numerous reports have demonstrated the improvement of glucose tolerance and insulin sensitivity in mouse models upon treatment with GDF15 protein. Two independent strains of transgenic mice overexpressing GDF15 have decreased body weight and fat mass, as well as improved glucose tolerance (Johnen et al., Nat. Med. 2007, 13:1333-1340; Macia et al., PLoS One. 2012, 7:e34868; Chrysovergis et al., Int. J. Obesity. 2014, 38: 1555-1564). Increases in whole-body energy expenditure and oxidative metabolism were reported in GDF15 transgenic mice (Chrysovergis et al., 2014, Id.). These were accompanied by an increase in thermogenic gene expression in brown adipose tissue and an increase in lipolytic gene expression in white adipose tissue. Mice lacking the GDF15 gene have increased body weight and fat mass (Tsai et al., PLoS One. 2013, 8(2):e55174). An Fc-fusion of GDF15 was shown to decrease body weight and improve glucose tolerance as well as insulin sensitivity in an obese cynomolgus monkey model when administered weekly over a period of six weeks (WO 2013/113008).
The effects of GDF15 on body weight are thought to be mediated via the reduction of food intake and increased energy expenditure. GDF15 may improve glycemic control via body weight-dependent and independent mechanisms.
Together, these observations suggest that increasing levels of GDF15 can be beneficial as a therapy for metabolic diseases. There is a need in the art for GDF15-based compositions that can be used to treat or prevent metabolic diseases, disorders, or conditions.